Low density bodies are generally used in various fields, taking advantage of their light weight, cushioning properties, heat-insulating properties, sound-absorbing properties, etc. The low density bodies most generally used are foams of synthetic resin such as polystyrene, polyurethane and polyethylene. Although these bodies are excellent in strength and processability, they have a problem in that when they are left to stand in natural environment, they keep their shape because are not biodegradable and, as a result, they spoil the appearance of the site for a long period of time and cause environmental pollution. Further, when they are dumped in reclaimed land, the land is filled in a short period of time because they are not biodegradable and they are bulky.
In addition, since these bodies cause high combustion heat, the combustion temperature is high when they are burnt in an incinerator to damage the incinerator and also to shorten the life thereof.
Under these circumstances, various biodegradable low density cellulose fiber bodies which have low combustion calory have been proposed. For example, there have been proposed, a process wherein a synthetic resin is mixed with cellulose fibers and the mixture is foamed [Japanese Patent Unexamined Published Application (hereinafter referred to as "J. P. KOKAI") Nos. Sho 55-23109 and Hei 3-269025, and Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J. P. KOKOK U") No. Sho 52-19152]; a process for producing a foamed product, wherein a foaming agent having a decomposition temperature of not above 100.degree. C. is incorporated into a composition comprising cellulose fibers compounded with a prescribed amount of a sticking agent made from an animal or plant source and an adhesive selected from among synthetic resin emulsions and rubber latices and the composition is foamed (J. P. KOKAI No. Hei 7-41588); a process for producing a sheet of paper having a low density and a high bulkiness by incorporating a granular foaming agent into cellulose fibers, making a base paper from the resultant mixture and foaming the paper by heating (J. P. KOKAI No. Hei 5-339898); bulky sheets of paper comprising cellulose fibers and calcium carbonate in the form of hollow spherical vaterite (J. P. KOKAI No. Hei 3-124895); and bulky sheets obtained by molding a mixture of a heat-fusible fibers and a crosslinked pulp obtained by reacting pulp with a crosslinking agent in the presence of a fiber-softening agent (J. P. KOKAI No. Hei 4-202895).
However, although the low density bodies obtained from the combination of cellulose fibers with the heat-fusible fibers have a high bulkiness, it has defects in that the number of the bonding points of the fibers is insufficient for obtaining a high bonding force and, therefore, the interlayer peeling easily occurs and that paper dusts are formed in the course of the production, handling and molding thereof to pollute the working atmosphere. The above-described process for obtaining the low density body by foaming with the foaming agent has defects in that the foaming cannot be easily controlled and the state of foaming is locally uneven to obtain a heterogeneous structure, and that when the foaming is excessive, the innerlayer peeling occurs to form edge dust at the peeled parts. The process wherein a nonbiodegradable resin or fiber is used has the above-described problem in disposing them.